Abstract
On 8th February 1996, in the north-western part of Andorra in the Pyrenees, the Les Fonts d’Arinsal (LFd’A) pure powder avalanche was triggered, descending some 1200 m to the bottom of the Arinsal valley and continuing up the opposite slope for about 200 m. This size 4–5 avalanche reached velocities of up to 80 ms−1, devastated 18 ha of forest, involved a minimum volume of up to 1.8 × 106 m−3 and caused major damage to eight buildings. Fortunately, no one was injured thanks to an evacuation, but 322 people lost their properties. This study describes the physical characteristics of the LFd’A avalanche path and provides data on earlier avalanches, the meteorological synoptic situation and snowpack conditions that generated the avalanche episode, the warning and preventive actions carried out, the effects and evidence of the large avalanche, and the defence system implemented afterwards. A discussion of the avalanche dynamics based on observations and damage, including the role of snow entrainment, the total lack of characteristic dense flow deposits, as well as the evidence of a two-phase flow (fluidisation and suspension), is presented. This case study is an example of a paradigmatic large, pure powder, dry-snow avalanche, which will be useful for model calibration.
Highlights
The winter of 1995 to 1996 was unusually intense in the Pyrenees
In the Catalan area of the range, from December 1995 to March 1996, the snowfalls doubled and even tripled the means calculated over a period of thirty years at half a dozen observatories, and the avalanche situation of 1996 was considered the most catastrophic of the second half of the 20th century [4]
These alerts led the national and local authorities and the police to close the road at 8:30 a.m. on 8th February to prevent more people accessing the area at risk
Summary
The winter of 1995 to 1996 was unusually intense in the Pyrenees. Six heavy snowfall episodes extended over two thirds of the length of the mountain range, from the Central Pyrenees in Aragon [1], across Andorra [2,3], to the Eastern Catalan Pyrenees [4,5]. Areny informed the minister in charge of territorial planning of the situation and of the need for urgent intervention to avoid fatal consequences These alerts led the national and local authorities and the police to close the road at 8:30 a.m. on 8th February to prevent more people accessing the area at risk. We review the warning and preventive actions carried out, the effects and evidence of the large powder avalanche, and the defence system implemented afterwards
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